Prune deformer set membership

To prune deformer set membership

Select the deformable objects whose currently unaffected points you want to prune from the deformation.
Select Edit Deformers > Prune Membership, and from the cascading menu select the deformer whose set you want to prune.
Note
Prune Membership only removes points from the deformation if they are currently not affected by the deformer. Therefore, if you try to prune the membership of an object whose points are all controlled by the deformer, you will receive the error message “No components could be pruned.”