A simple way is to use datapump for this. You can even directly use impdp with a databaselink to the own database to do the “close”, like:
impdp system/manager schemas=A remap_schema=A:B network_link=MY_OWN_DB
Note that if you use dblink no parallel will be possible. In some cases it will be faster if you do expdp to a dumpfile with parallelism and then import it again with impdp in parallel too.