No it's actual hardware coherent memory across the system. At a high level it is the same way two cores/caches are connected within one chip, or the same way two sockets are connected on the same board. Just using cables instead of wires in the chip or on a board.

This system has SMP ASICs on the motherboards that talk to a couple of Intel processor sockets using their coherency protocol over QPI and they basically present themselves as a coherency agent and memory provider (similarly to the way that processors themselves have caches and DDR controllers). The Intel CPUs basically talk to them the same way they would another processor. But out the other side these ASICS connect to a bunch of others all doing the same thing, and they use their own coherency protocol among themselves.