Bitcoins are like cash - you also cannot go to the central bank and say "hey, this 100$ bill was scammed from me, please reverse/dispute it". Just go to the police and/or get a lawyer.
In fact its the same as with bank transfers in most of the world (outside USA).
At least in most European countries, the only way to "reverse" a bank transfer is to sue the counter-party to force them to send you the transfer back.
It's only in the USA and maybe some other places which have a banking culture similar to the USA that you can go to your bank and reverse the transaction. And for all countries for credit cards and direct debit, but that's a different story. I am talking about wire transfers.
BTW, can someone, who knows the USA banking system well, tell me is a Fedwire in the USA reversible in case of a scam, without suing?
I mean this:
http://en.wikipedia.org/wiki/Fedwire