Got this question twice this week so I’d say it is blog worthy.  How to configure a Hyper-V server to be remotely managed (manage stand alone server or across domains).  You might also consider reviewing the ACLs he describes if you are troubleshooting some anomaly in a trusted domain environment.

John Howard has instructions but he also has written a tool specifically more making the changes easier.

John Howard - Hyper-V and virtualization blog : Configure Hyper-V Remote Management in seconds