Is MDM Password History stored on device or on server?

I was wondering if the password history is stored on the iOS device or on the server when the password history policy is implemented through MDM (specifically, Exchange ActiveSync)? I have done a lot of reading and while I would assume that it is stored on the device, I wanted to make sure. And if it is stored on the device, can anybody say how? Same with server? (I.e. hash/salt)