In many modelling tools the user can define multiple diagrams or views of the entities and associations in a model. This makes it easier to organise and layout complex Domain Models as each diagram can contain a subset of the entities and associations in the Domain Model, allowing you to create different diagrams for different purposes and with different scopes.
There is still one Domain Model (per module) and when you select the properties of any given entity you still see everything in the model. But in the diagram you can add or remove entities and associations which exist in the model.
This generalised approach would also go some way to addressing other request for improved usability of the existing domain model diagram.