Glad to hear that someone has taken this up. It would be great if nginx support was included.
To purge page http://mysite.com/node/1 from the nginx cache you just need to visit http://mysite.com/purge/node/1. The "/purge/" part is configurable, but that seems to be the convention. http://labs.frickle.com/nginx_ngx_cache_purge/
There are already two Wordpress modules that support nginx cache purging so a Drupal one would be great. (http://wordpress.org/extend/plugins/nginx-manager/ and http://wordpress.org/extend/plugins/nginx-proxy-cache-purge/)