To all those of you that have Web pages - a little help, please.

My Web site is up and running - no problems. However, as I'm continually 
changing it as I learn my way into Web page authoring, I've found a problem.

My company has a firewall through a proxy server, which also caches accessed 
Web pages to save time. So when I change my web page, the  proxy server won't 
give me the new page, as it still has the old one cached.  I'm told there is 
a mechanism to put a "validity" stamp on a web page, so  that the proxy knows 
that it is to be refreshed, and will download the new  page from my Web 
Server. But I don't know how to do it. Help, anyone ?

TIA,

Phil Yates
www.hawksoftware.ndirect.co.uk
"Little does he know that if he knew how little I know, he'd know a little."