Its a user/browser issue rather a webpage one. If you've put a meta tag forced refresh in there correctly, then there isn't much you can do other than recommend that they change proxy, do a full refresh (usually a ctrl-F5 or shift-F5, rather than a regular F5)
---------- Post added at 20:26 ---------- Previous post was at 20:19 ----------
BTW, for reference the proper code is:
<meta http-equiv="pragma" content="no-cache">
Also, you might want to try the stuff in here...
http://www.htmlgoodies.com/beyond/re...le.php/3472881