60万req/時のアクセスを捌くために外部サーバーのコンテンツもキャッシュをしたい。

Wordpress + Nginx + php-fpm の環境でNginxのリバースプロキシ+ブラウザーキャッシュを使用しています。

60万req/時を捌きたいのですが外部リンクからのjavascript、画像だったりをキャッシュしたいのですが
こういうのは可能なのでしょうか。

JMeterでテストを行うと自サーバーのコンテンツはエラーが無く順調なのですが、外部から引っ張ってきてるものがエラーを出してしまっている状況です。

参考になるか分かりませんが下記がNginxのコンフィグになります。
何かご教授いただければよろしくお願いします。

nginx.conf

user  nginx;
worker_processes  auto;

worker_rlimit_nofile  150000;

events {
    worker_connections  65535;
    use epoll;
    multi_accept on;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    sendfile        on;
    tcp_nopush      on;

    server_names_hash_bucket_size 64;

    keepalive_timeout  0;

    gzip  on;
    gzip_disable "MSIE [1-6]\.";
    gzip_proxied any;
    gzip_min_length 1024;
    gzip_comp_level 6;
    gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript application/javascript;

    proxy_max_temp_file_size    2048M;
    proxy_buffers               100 8k;
    proxy_buffer_size           8k;
    proxy_cache_path  /var/cache/nginx levels=1:2 keys_zone=czone:15m max_size=60g inactive=7d;
    proxy_temp_path   /var/tmp/nginx;
    proxy_cache_key $scheme://$host$request_uri;

    proxy_set_header  Host               $host;
    proxy_set_header  X-Real-IP          $remote_addr;
    proxy_set_header  X-Forwarded-Proto  https;
    proxy_set_header  X-Forwarded-Host   $host;
    proxy_set_header  X-Forwarded-Server $host;
    proxy_set_header  X-Forwarded-For    $proxy_add_x_forwarded_for;

    set_real_ip_from    127.0.0.1;
    real_ip_header      X-Forwarded-For;

    upstream xxx {
        ip_hash;
        server 127.0.0.1:8081;
    }

    include     /etc/nginx/conf.d/*;
}

conf.d/default.conf

server {
    listen       80;
    server_name  111;

    charset utf-8;
    access_log  /var/log/nginx/access_log main;
    error_log   /var/log/nginx/error_log;

    root        /var/www/chroot-website;

    client_max_body_size        1G;

    add_header  X-Cache $upstream_cache_status;

    location /nginx_status {
        stub_status on;
        access_log  off;
    }

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt { access_log off; log_not_found off; }

    location ~ \.ico$ {
        log_not_found off;
        access_log off;
        expires max;
    }

    location ~ \.(css|js)$ {
        proxy_pass http://xxx;
        charset  UTF-8;
        access_log off;
    }

    location ~* \.(jpe?g|gif|png|ico|woff|svg|swf|inc)$ {
        proxy_pass http://xxx;
        access_log  off;
    }

    location /wp-content/uploads {
        proxy_pass http://xxx;
        access_log  off;
    }

    location ~ /\. {
        deny          all;
        access_log    off;
        log_not_found off;
    }

    location = /wp-config.php {
        deny        all;
        access_log  off;
    }

    location ~ .*\.php {
        proxy_pass http://xxx;
    }

    location / {
        set $do_not_cache 0;
        if ($http_cookie ~* "comment_author_|wordpress_(?!test_cookie)|wp-postpass_|wordpress_logged_in" ) {
            set $do_not_cache 1;
        }
        if ($request_method != GET) {
            set $do_not_cache 1;
        }

        # mobile setting
        include /etc/nginx/mobile_cache_setting;

        proxy_cache_valid       200 302 180m;
        proxy_cache_valid       404 7d;
        proxy_no_cache          $do_not_cache;
        proxy_cache_bypass      $do_not_cache;
        proxy_cache             czone;

        proxy_cache_key         $scheme://$host$uri$is_args$args;
        proxy_pass              http://xxx;
    }
}

server {
    listen      8081;
    server_name 111;

    root        /var/www/chroot-website;
    index       index.php;

    access_log  /var/log/nginx/access8081.log;
    error_log   /var/log/nginx/error8081.log;

    location / {
        try_files $uri $uri/ /index.php?q=$uri&$args;

        location ~ /wp-content  {
            access_log  off;
            include     /etc/nginx/php_exec;
        }
        location ~ /wp-includes {
            access_log  off;
            include     /etc/nginx/php_exec;
        }
        location ~ /wp-cron.php {
            access_log  off;
            include     /etc/nginx/php_exec;
        }
        location ~ /wp-comments {
            access_log  off;
            include     /etc/nginx/php_exec;
        }
        location ~ /wp-admin {
            access_log  off;
            include    /etc/nginx/php_exec;
        }
        location ~ /wp-login.php {
            access_log  off;
            include     /etc/nginx/php_exec;
        }
        include /etc/nginx/php_exec;
    }
}

nginx/php_exec

location ~\.php$ {
    expires          off;
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_pass     unix:/var/run/php-fpm/php-fpm.sock;
    fastcgi_index    index.php;
    fastcgi_param    SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    include          fastcgi_params;
}