Is looking at a a strategy of renaming the cache directory first a possible way to reduce the race condition. If you move the directory, all existing requests will still finish reading and/or writing to the renames space. And all new requests will attempt to recreate the cache folder and write files to the new location.
This ensure that's other threads will not try and write new cache files to the version of the cache we are trying to remove. I'm not convinced that rename is an atomic operation on all filesystems but it has to reduce the window from seconds to microseconds.
However the reports of this happening during an upgrade appears strange. That's a single threaded process that should always finish clearing the cache before it move on. The only thought is that there is a file it can't remove and it just continues to attempt to remove the folder. If that is true, renaming the folder should remove that issue as well.
Maybe the folder couple be moved into the trash bin and the trash code could clean it up. But that might be taking it too far.