1) Shutdown all datbases that are running on the box using the +ASM instance for storage management
2) Use emca -x <sid> to remove the Database Console for each instance
3) Remove the service for the instances
ORADIM -DELETE -SID <sid> and ORADIM -DELETE -ASMSID <asm sid>
to delete the services for the database(s)/instances
If using RAC ... remove the asm service with .... svrctl remove asm -n <nodename>
3) Remove the PFILEs / SPFILEs and password files (orapw<sid>) for the ASM and Databases
Default location: <ORACLE_HOME>/DATABASE
4) Delete / Remove any non ASM supporting directories
BACKGROUND_DUMP_DEST
USER_DUMP_DEST
CORE_DUMP_DEST
etc
5) Format the ASM disks