  The construction of symmetry breaking differential operators, using invariant
pluri-harmonic polynomials, due to T. Ibukiyama in the context of the Siegel
upper half space, is extended for scalar representations to general Hermitian
symmetric spaces of tube-type. The new context is described in terms of
Euclidean Jordan algebras and their representations. As an example, new and
explicit differential operators are obtained for the restriction from the tube
domain over the light cone to the product of two upper half-planes.
