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