This was a patent by Siemens for a copy-protection scheme where there's a descrambler in front of the prefetch queue. Each CPU would have a unique permutation - this means that software could be tied to a specific CPU. Just scrambling 16 bits gives you something like 16! = 20,922,789,888,000 possibilities, but this system also lets you invert bits too, so ... it's a lot. It's also cryptographically chickenshit, so it would have been cracked immediately https://patents.google.com/patent/US4633388A/en