I have setup a reverse proxy that is working beautifully, but I don't know how to tell if a page is being served from cache or if the reverse proxy is going to the source server to retrieve the page. It's imperative that I reduce load on the source server by caching.

I'd like to be able to find out a % of pages that are served from the proxy's cache. Here is my setup in httpd.conf:

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule cache_module modules/mod_cache.so
LoadModule mem_cache_module modules/mod_mem_cache.so

ProxyPass / http://www.google.com/
MCacheMaxObjectCount 2000
MCacheMaxObjectSize 200000
MCacheMaxStreamingBuffer 200000
MCacheMinObjectSize 0
MCacheRemovalAlgorithm LRU
MCacheSize 700000

I have it setup on my localhost for now and when I hit http://localhost I get Google, but I don't know if it's from the proxy's cache.