How oracle internal reverse search index object.

How oracle can quickly to allocate a entry in index when user to delete a record in main table use rowid?

For a sample, we have a big table with million rows, each row have same value for column called Status, also have index on column Status. When delete a row using rowid, such delete statement can be executed very quick, it does not like oracle to scan full index to allocate the rowid value in index.

Oracle must have a efficient method to quickly allocate the corresponding entry in index, then mark this entry as deleted. Anyone know how Oracle internally handle such reverse search?