Threshold photoemission magnetic circular dichroism of perpendicularly magnetized Ni films on Cu(001) was measured in total electron yield and used to observe the magnetic domain structure in a photoemission electron microscope. Spin-polarized relativistic Korringa-Kohn-Rostoker Green's function calculations including a dynamical mean-field theory approach within the one-step-photoemission model reproduce the measured asymmetry in the photocurrents for left and right circularly polarized light. In addition, a three-step photoemission model calculation based on the same ab initio calculation is used to quantitatively explain the MCD effect near the photoemission threshold.