Functionality can be implemented in an operating system to increase the granularity of isolation for objects. A domain can be defined to represent each of different entities (e.g., different departments or work groups). User identifiers and/or user credentials can be associated with the appropriate domain or domains. An administrator can then define a set of rules that govern operation(s) that can be performed on the objects based on the domains. Processes running on a system will inherit the domains of a user account logged into the system. When a process running on the system attempts to perform an operation on an object, an operating system process evaluates the domain isolation rules with an identifier of the object and a domain identifier to determine whether the operation is permitted to proceed.