Create an organizational unit (OU) in Active Directory specifically for your remote desktops.
To prevent group policy settings from being applied to other Windows servers or workstations in the same domain as your remote desktops, create a GPO for your Horizon 8 group policies and link it to the OU that contains your remote desktops.
See the Microsoft Active Directory documentation on the Microsoft TechNet Web site for information on creating OUs and GPOs.