Yep, Ctrl-F5 works on every browser. ...or at least all the ones I've tried. <img src="{SMILIES_PATH}/icon_razz.gif" alt=":P" title="Razz">
What I do when uploading a new build for testing might not be the most user-friendly way, but it works. I upload my game to a new link, usually by posting the game in a folder with the date as a name.
For example, http://yoururl.com/randomgame/5-26-15/index.html, and then next time I upload I use a different date.
Then I would update the link on the forums, or you could send the new link to the user. The problem is you can't save it as a bookmark, which would be the easiest for a client.