UNDO Data for a LOB Segment is Kept within the LOB Segment Space

Never realized this before. See metalink note:
How to determine the actual size of the LOB segments and how to free the deleted/unused space above/below the HWM [ID 386341.1] for details.

Using command to free the space:
alter table <tablename> modify lob(<lob_column>) (shrink space [cascade]);