Resonantly excited secondary emission of light (RSE) in GaAs/AlGaAs superlattices gives a direct proof for the stability of coherent Bloch dynamics beyond the optical coherent regime. The polarization analysis of the RSE signal confirms its nonlinear origin resulting from coherent intraband density dynamics. lt is shown that the intraband coherence of Bloch oscillations (BO) persists after momentum scattering of the photoexcited states. A variation of emission angle and ex-citation density allows to distinguish two momentum scattering processes contributing to the RSE. A static disorder mediated contribution is restricted to directions near the reflection direction. A further contribution of carrier induced momentum scattering is resolved in directions well separated from diffraction directions. The dependence of the RSE as a function of an external electric field demonstrates an enhancement of momentum scattering with increasing field.