  We present experimental and numerical studies of nonlinear magneto-optical
rotation (NMOR) in rubidium vapor excited with resonant light tuned to the
$5^2\!S_{1/2}\rightarrow 6^2\!P_{1/2}$ absorption line (421~nm). Contrary to
the experiments performed to date on the strong $D_1$ or $D_2$ lines, in this
case, the spontaneous decay of the excited state $6^2\!P_{1/2}$ may occur via
multiple intermediate states, affecting the dynamics, magnitude and other
characteristics of NMOR. Comparing the experimental results with the results of
modelling based on Auzinsh et al., Phys. Rev. A 80, 1 (2009), we demonstrate
that despite the complexity of the structure, NMOR can be adequately described
with a model, where only a single excited-state relaxation rate is used.
