Oracle Internals Notes
Oracle maintains an unrecoverable SCN for each datafile.
It is the SCN of the most recent change to that datafile by a NOLOGGING operation.
The term reflects the fact that NOLOGGING operations were called UNRECOVERABLE operations under Oracle7.
The unrecoverable SCN (and time stamp) for each datafile is recorded in the datafile record section of the controlfile.
It is updated by a controlfile transaction
whenever the datafile is affected by a NOLOGGING operation,
unless event 10359 has been set.
The unrecoverable SCN is used by RMAN to determine whether a datafile
has been affected by a NOLOGGING operation since the last full or incremental backup of that datafile.
It is not used for any other purpose.