In such a case, the server can tell the browser (in our case intercepted by the caching proxy) to not cache the file or for it to expire from cache immediately. It's there in http headers.
The first is done by setting the "Cache-Control: no-cache" or the "Pragma: no-cache" headers and the second is set by the "Expires:" header [1].
Sharad [1] http://www.httpwatch.com/httpgallery/caching/ -- Mailing list guidelines and other related articles: http://lug-iitd.org/Footer
