The NRZ signal sent is fed with the clock signal through an XOR gate, creating a strobe signal.
From the en.wikipedia.org
For the logic gate, see XOR gate.
From the en.wikipedia.org
More generally, changing an odd number of inverters on an XOR gate produces the dual gate, an even number leaves the gate's functionality unchanged.
From the en.wikipedia.org
For the AND and OR gates the location of each inverter matters, for the XOR gate it does not, only whether there is an even or odd number of inverters.