Hot fire, stoked with forced air. HDDs rely on magnetism, bringing the platters above the Curie temperature destroys all information - 570 °C (1,060 °F) . SSDs, I'm actually not sure, but I imagine a bed of white-hot coals will render any electrical charge in those tiny cells undecipherable. Heat increases the ability of electrons to tunnel (jump out of potential wells) so at some temp, the traps will leak all their charge.
I'm not a semiconductor guy so I'm not making any claims.
