How can I force window.location to make an HTTP request instead of using the cache?

You could just add a random parameter to the page URL in order to have the browser issue a new request.

So instead of using

 window.location = "my.url/index.html";

use

 window.location = "my.url/index.html?nocache=" + (new Date()).getTime();

You can use location.reload with a true argument, which will always bypass the cache.

window.location.reload(true);