This annotation effectively takes information out of the cache, removes single value from cache. These annotation is
useful when you know that a value has been made stale and you want to force it to refresh on the next time it is
referenced in a ReadThroughSingleCache method.
A namespace that is added to the key as it is stored in the distributed cache. This allows differing object that
may have the same ID to coexist. This value must be assigned.
Returns:
the namespace for the objects cached in the given method.