Fixing Purge behavior with nested materials

When using any kind of purge tool it also purges materials that are nested into Geometries or multi materials.
When you purge materials , you also purge materials that are only used for those geometries or materials but aren't physicaly applied to any material.
Examples:
Grass and fur, the grass material is only made to be applied to the grass and nothing else)
Double sided materials for curtains.
Multi sub materials
Layered materials
...