Since Intel makes huge dies, it won't be a problem to squeeze some L4 (fourth level cache) to boost memory bandwidth and lower the latency in some of its Haswell SKUs. The Haswell variant that is internally known as Crystal Well offers much larger L4 cache.
The size of the cache is not clear, but we heard that there can be up to 64MB cache dedicated for graphics. This does sound a bit too much,
From the mouth of engineers in the Far East, it could be that the L4 cache remains dedicated only for the GPU, but the other independent sources claim that L1, L2, L3 and L4 memory will be shared between CPU and GPU. We will have to look into which of these two theories is right.
Crystal Well is reserved for GT3 based highest end processors from Intel, and we have heard that it remains an exclusive technology for Core i7 processors. You will have to pay up to enjoy it.
L4 cache is nothing new to the GPU world and consoles have been using such cache to make the texture and antialiasing faster on them. Dedicated cache on GPUs has been considered by Nvidia and ATI (even before the 2006 AMD acquisition) for years. The main obstacle was always that the transistor count for GPU cache memory was very high and it would result in a huge chip, something that semiconductor manufacturers tend to avoid.
It will be interesting to see Haswell Crystal Well in action when it launches later this year, but we are certain that we can see a huge performance leap from Intel Ivy Bridge 4000 series graphics.