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IBM Power8 and Power9 used Centaur chips which had similar "last level cache" onboard.

Because it is last level before the actual ram chips, no coherency involved.

Since it is attached to the memory controller, one could argue that it is truly the final level of the cache hierarchy and the term infinity is not only a marketing term.

But then you could add another level of slower (but still faster than RAM) and larger cache. So it is after all the CPU caches, but the first of all the memory caches. A more mathematically correct name would be L_omega.

Sounds a bit like a tightly coupled memory (TCM) in an embedded CPU; Fast single cycle RAM shared across the system.

This is quite exactly the opposite of TCM in fact

Thank you!