  Neutrino-nucleus elastic scattering ($\nu {\rm A}_{el}$) provides a unique
laboratory to study the quantum-mechanical (QM) coherency effects in
electroweak interactions. The deviations of the cross-sections from those of
completely coherent systems can be quantitatively characterized through a
coherency parameter $\alpha ( q^2 )$. The relations between $\alpha$ and the
underlying nuclear physics in terms of nuclear form factors are derived. The
dependence of cross-section on $\alpha ( q^2 )$ for the various neutrino
sources is presented. The $\alpha ( q^2 )$-values are evaluated from the
measured data of the COHERENT CsI and Ar experiments. Complete coherency and
decoherency conditions are excluded by the CsI data with $p {=} 0.004$ at $q^2
{=} 3.1 {\times} 10^{3} ~ {\rm MeV^2}$ and with $p {=} 0.016$ at $q^2 {=} 2.3
{\times} 10^{3} ~ {\rm MeV^2}$, respectively, verifying that both QM
superpositions and nuclear many-body effects contribute to $\nu {\rm A}_{el}$
interactions.
