Sometimes when I make small changes to a website, I notice that certain browsers are very stubborn about downloading the page again.  Both F5 and CTRL-R are worthless and the only way to fix it is to go through the options and manually tell it to clear the cache.  I've used PHP before to send a cache-flush header, but is there a simpler or better way?
How can I cause a browser to download a new copy of a web page when it thinks that its cached copy is still valid?
cache