If you are ever reinstalling on an ASM and you can't select your disks in the DBCA because they are already member of the diskgroup, you have to delete the label before

dd if=/dev/zero of=/dev/oracleasm/disks/MYDB_ASM_ARC_1 bs=1024 count=100
dd if=/dev/zero of=/dev/oracleasm/disks/MYDB_ASM_DB_1 bs=1024 count=100