Moving a lob segment from on tablespace to another is a little tricky ,And it is little different than moving a table from a tablespace to another.
The Syntax for moving LOB segments would be
alter table tablename move lob (CONTENTS) store as (tablespace tablespacename);
EXAMPLE:
alter table sys.abc move lob (CONTENTS) store as (tablespace users);
The index associated with the lob segments cannot be moved to another tablespace that is indifferent from the lob segment tablespace.
