Particularly the main piece of virtualization is an added level of indirection to the page table walking hardware.
There's some IOMMU stuff that can be bought off the shelf (and ARM's SMMU for this is really good actually), but I imagine Apple would build their own (or acquire it) looking at the rest of their IP blocks.
Edit: Actually I'm not even sure if they could pull an SMMU in. Do we have confirmation that they're using AXI/CHI or do they have something else for their NoC protocol?