corrupt datafile

 Hello,

I have a corrupt datablock on the system tablespace.  I'm getting these errors:

ORA-05178: Oracle data block corrupted (file #1, block # 1391581)

  ORA-01110: data file1: '/ora1/oradata/xxxxx/system01.dbf

I've tried different things  in RMANsuch as

sql 'alter database datafile 1 offline'

restore datafile 1;

recvover datafile 1;

sql 'alter database datafile 1online;

 However, I think this method is assuming that the datafile in the RMAN backup is not corrupted.  This file/block has been corrupted for some time.  Do we need to find the backup without the corrupted file?  Or can this file be recreated?

thanks in advance.

Rae