  We discuss finite difference techniques for hyperbolic equations in
non-trivial domains, as those that arise when simulating black hole spacetimes.
In particular, we construct dissipative and difference operators that satisfy
the {\it summation by parts} property in domains with excised multiple cubic
regions. This property can be used to derive semi-discrete energy estimates for
the associated initial-boundary value problem which in turn can be used to
prove numerical stability.
