Would an ISIS-issued currency be accepted globally?

For a currency to be accepted worldwide, its monetary and banking system has to be accepted worldwide. If the latter holds true, then it (Isis) would most likely start with amassing foreign currency in their ledger, and trade using that. No one has any use for an Isis issued note, so it would be worthless in the initial few years, till such time a demand for their currency (via trade) came into being.