When I worked for Key Bank Internet Banking support a few years ago, we used to advise customers to change the cache behavior ("Check for newer versions of stored pages...") of their browsers to "Every visit to the page". This is found under Tools>Internet Options...>Temporary Internet Files>Settings...
Of course getting your visitors to make this change might be easier said than done, especially once they realize it can really slow down their browsing on graphics-intensive sites. (And personally, I hate to force reloads of pages that use TinyMCE to create WYSIWYG text boxes!)