It is a new inter-chip connection that will be used in the Exascale Heterogeneous Processor (EHP). Coherent fabric is primary interconnect for IP on AMD SOCs, APUs, CPUs and GPUs beginning with the next generation CPU SOC and followed by the Greenland GPU ASIC. Incoherant fabric, on the other hand, is something worn by loud American tourists and is sometimes called a Hawaiian shirt.
AMD's GMI - Global Memory Interconnect, extends the coherent fabric between chips on the same multi-chip module (MCM) package. The coherent fabric extends between packages using combo phys which also support PCIe interconnection.
All this sounds rather complicated, but is basically a faster way for Zen SoC to talk to the Greenland Die on future processors.
Coherent fabric will speed up the communication in Zen CPUs between the cores and cache, host controllers, eg. USB, SATA or GbE, memory controllers, PSP, timer, counter, ACPI or legacy interface, combo phys and GMI layers. GMI phys of Zen die will talk directly with GMI phys of Greenland HBM 2.0 graphics die and uses coherent fabric too.
Our industry sources did not want to go into the specifics of achievable speeds of this interconnect, but the promise of a significant improvement is there. And of course the upcoming AMD's 16 core Heterogenous EHP Processor will benefit from the fast coherent fabric interconnect.