Here's the config:
 location ~ ^/purge(/.*)$ {
                       allow 127.0.0.1;
                       allow 192.168.0.0/16;
                       allow 72.12.74.93;
                       deny all;
                       proxy_cache_purge	staticfilecache   "$scheme://$host$1";
        }
Posted at Nginx Forum: http://forum.nginx.org/read.php?2,61318,63815#msg-63815