  We provide an elementary proof of geometric synchronisation for scalar
conservation laws on a domain with Dirichlet boundary conditions. Unlike
previous results, our proof does not rely on a strict maximum principle, and
builds instead on a quantitative estimate of the dissipation at the boundary.
We identify a coercivity condition under which the estimates are uniform over
all initial conditions, via the construction of suitable super- and
sub-solutions. In lack of such coercivity our results build on Lp energy
estimates and a Lyapunov structure.
