We use the discrete dipole algorithm (DDA) to calculate the light-scattering properties from arbitrarily shaped, heterogeneous agglomerated debris particles to study the performance of effective medium approximations. The homogenization of the material properties of the particle has little effect on the orientation-averaged intensity phase function. However, there are some differences in the polarization response. While the structure of the linear-polarization response is not significantly different between the homogeneous and heterogeneous cases, the amplitude of the polarization tends to show a dependence on particle heterogeneity. The Bruggeman mixing rule tends to reproduce the heterogeneous results marginally better than using the average of two distributions of the individual homogeneous components. In addition to the irregularly shaped particles, we also calculated scattering properties of equivalent-volume, homogeneous spheres. As expected, the errors due to assuming homogeneous particles are overwhelmed by those introduced by assuming the irregularly shaped particle may be replaced by an equivalent spherical particle.