Na-23 and Li-7 relaxation measurements were used over a broad range of frequencies to determine ion diffusion in aqueous dispersions of Montmorillonite and Laponite clays. In agreement with our previous Brownian dynamics simulations of ion diffusion and relaxation in such heterogeneous system, the spectral densities of these 3/2 spin nuclei exhibit a transition between two dynamical regimes characterized by a plateau and a power-law decrease. The frequency crossover is determined by the spatial extent of microdomains composed of partially oriented clay particles. This result illustrates the potentiality of nuclear quadrupolar relaxation as a sensitive probe of the spatial propagation of orientational order within heterogeneous systems limited by charged interfaces.