  We investigate a general class of models for swarming/self-collective
behaviour in domains with boundaries. The model is expressed as a stochastic
system of interacting particles subject to both reflecting boundary condition
and common environmental noise. We rigorously derive its corresponding
macroscopic mean-field equation, which is a new type of stochastic partial
differential equation due to the presence of common noise. The approach relies
on a compactness argument, in which we first establish the tightness of the
empirical measures associated with the particle system and then demonstrate
that the time marginal of the limit measure is a solution to the mean-field
equation.
