In some older IBM-built processors (channel controllers, the various iterations of the CSP), an xor of something against itself also had the effect of safely cl

In some older IBM-built processors (channel controllers, the various iterations of the CSP), an xor of something against itself also had the effect of safely clearing a stored bad parity without triggering a parity check from reading the operand. You would see strategic clearing in this manner done by system software or firmware during error recovery or early initialization.