I used a tool called Firebug, which is a Firefox plugin - and the .xml is being cached at the browser.
This is actually a good thing, because it means there are fewer requests to the server.
To clear the cache, in IE, go to Tools > Internet Options > Delete > Temporary Internet files. Then, refresh the page and your changes should be visible.
If you're using Firefox, you can use Tools > Options > Advanced > Network > Offline storage > Clear Now.
Clearing the browser cache and then refreshing will confirm or cancel the idea that the issue is related to browser caching. If it is just caching, you can clear the cache manually as you're working on the site and then once it goes live, it should be fine.
So - modify the .xml, clear the browser cache, and see if your changes are there.