A method and/or computer program that incorporates isolation principles of separate address spaces and enforces the principles with a compiler and supporting runtime through a language-based model is disclosed. This approach significantly lowers the required overhead and retains the beneficial qualities of the scalable, isolated model. The model is implemented in a programming language where memory-based state is partitioned into a plurality of domains where the variables inside of a domain are isolated from external components. Agents are introduced inside of the domain and act on behalf of clients outside of the domain. The agents communicate with their clients via message-passing to enforce the isolation of the domain state. The domain-based isolation addresses the partitioning of memory-based state without the introduction of separate processes. Domains can also be used in conjunction with a distributed model either within a single computing device or between computing devices.