  New evidence is presented in favor of irreversible decoherence as the
mechanism which leads an initial out-of-equilibrium state to quasi-equilibrium
in nematic liquid crystals. The NMR experiment combines the Jeener-Broekaert
sequence with reversal of the dipolar evolution and decoding of
multiple-quantum coherences to allow visualizing the evolution of the
multi-spin coherence spectra during the formation of the quasi-equilibrium
states. We vary the reversion strategies and the preparation of initial states
and observe that the spectra amplitude attenuate with the reversion time, and
notably, that the decay is frequency selective. We interpret this effect as
evidence of "eigen-selection", a signature of the occurrence of irreversible
adiabatic decoherence, which indicates that the spin system in liquid crystal
NMR experiments conforms an actual open quantum system
