The file and its parent directory are set to 777, but there is no information in the file except for the header,
<?xml version="1.0" encoding="utf-8"?>
I guess I am still not getting it. Even if the cache file was working, which it apparently isn't, in order for the information to get there in the first place, the server still has to deliver the geocode information for all map points at least once, no?
You seem to be suggesting that it would be a reasonable solution for the cache to eventually get all correct entries by adding a few more good responses each time a page is refreshed?