I would strongly look at Clojure's implementation of Atoms, Agents and Refs. IMO that is the best isolation of mutation I've seen in any language.

What do I mean by isolation of mutation? As stated above, all applications end up needing global shared mutable state (usually it lives in databases, but doesn't have to). So Rich Hickey created mechanisms to do such things safely and concisely.

Exactly. Clojure is a great example, although it doesn't offer a complete solution: atoms/agents/refs are either not general enough or not performant enough to handle many data structures well.