Many proxy servers can't read META tags. You just have to hope that the correct page is saved in the proxy's cache. HTTP headers control how both browser and proxy caches handle your Web pages. They are invisible in HTML and usually generated automatically by your Web server. Don't assume that all or even most proxy servers are configured this way.
Many servers never look at a page's HTML code at all.
You'll have to use actual HTTP headers to be sure that AOL's 27 million members see your updated pages. AOL's Webmaster Info section describes their caching system in detail. HTTP Headers Are Reliable HTTP headers are the only way to reliably control caching. You can set page expiration dates and page caching instructions using HTTP headers. Learning how may take some time and research though.