  We present the result for the invariant B_K factor of K0-anti-K0 mixing in
the chiral limit and to next-to-leading order in the 1/Nc expansion. We
explicitly demonstrate the cancellation of the renormalization scale and scheme
dependences between short- and long-distance contributions in the final
expression. Numerical estimates are then given, by taking into account
increasingly refined short- and long-distance constraints of the underlying QCD
Green's function which governs the B_K factor.
