Which cache should the cache controller control?
			• L1 cache is already very busy with CPU traffic • L2 cache also very busy… • L3 cache doesn’t always have the current value for a cache line 1. Although L1 cache is normally write-through, L2 is normally write-back 2. Some data may bypass L3 (and perhaps L2) cache (eg when stream-prefetched) – In Power4, cache controller manages L2 cache – all external invalidations/requests – L3 cache improves access to DRAM for accesses both from CPU and from network