You can delete or you can deactivate elements for the domain you are not interested in. Boundary conditions which are completely surrounded by inactive/deleted elements will be excluded/eliminated. Process variables (e.g. heads, pressures etc.) will be adopted for all nodes which are not completely surrounded by inactive/deleted elements. Material properties are assigned to the elements. Accordingly, if you deactivate/delete elements corresponding material properties will be excluded/eliminated. In contrast, all material properties will be maintained for all elements you do not exclude/eliminate.
