It is potently magical, so no normal magical weapon would do the trick. Perhaps a Sharpness of Vorpal admantium blade or ax could do it. Since it travels to Cald, sending it to the Plane of Fire might destroy it. Disjunction can work, but given the power of the item, its saves are likely high.
There is no easy way to destroy it, but that is in line with a magic item crafted by a caster of 17+ level using a 9th level spell (Gate).