Purging tiles from hash grid cache may affect other tiles in current implementation.

[Hineven]

In GI10 the PurgeTiles kernel remove outdated tiles by resetting their hash values in the hash table to 0 (not populated).
I suspect that if there're multiple tiles active within the same bucket, the removal of i-th tile may cause the next query of the succeeding i+1 th...kth tile to fail and eventually re-allocate tiles, losing history radiance values.