  The need to smoothly cover a computational domain of interest generically
requires the adoption of several grids. To solve the problem of interest under
this grid-structure one must ensure the suitable transfer of information among
the different grids involved. In this work we discuss a technique that allows
one to construct finite difference schemes of arbitrary high order which are
guaranteed to satisfy linear numerical and strict stability. The technique
relies on the use of difference operators satisfying summation by parts and
{\it penalty techniques} to transfer information between the grids. This allows
the derivation of semidiscrete energy estimates for problems admitting such
estimates at the continuum. We analyze several aspects of this technique when
used in conjuction with high order schemes and illustrate its use in one, two
and three dimensional numerical relativity model problems with non-trivial
topologies, including truly spherical black hole excision.
