It is only possible for zil due to the small dag and 1/4th fitting into the on die cache.
The rx580 had an adjustable TLB cache that was modified when the card was in compute mode. Not sure about the 6800. We don't have that card yet.
he means the infinity cache from the new AMD series, because it is 256mb and this is 1/4 of the Zil DAG. But as i said, this infinity cache is not useable by any mining software (at the moment)