Which is why the interconnect fabric adds the source address based on who made the request.

Even hardware IP blocks don't have the ability to send packets from arbitrary addresses. You can send to anywhere you want, but you can't lie about who made the request. Which allows access control to be enforced at the receiving end.

That "something you are" as well as "something you know" factor prevents any capability from being spoofed, since the identity of the device initiating the request is part of the capability.