Delete Old Archivelogs from missing database
We finally deleted the files manually and OEM is fine.

We ran this query to get the delete scripts:

SELECT 'alter diskgroup ' 
       || gname 
       || ' drop file ''+' 
       || gname 
       || Sys_connect_by_path(aname, '/') 
       || ''';' a 
FROM   (SELECT b.name            gname, 
               a.parent_index    pindex, 
               a.name            aname, 
               a.reference_index rindex, 
               a.system_created, 
               a.alias_directory 
        FROM   v$asm_alias a, 
               v$asm_diskgroup b 
        WHERE  a.group_number = b.group_number) 
WHERE  alias_directory = 'N' 
       AND system_created = 'Y' 
START WITH ( MOD(pindex, Power(2, 24)) ) = 0 
           AND rindex IN (SELECT a.reference_index 
                          FROM   v$asm_alias a, 
                                 v$asm_diskgroup b 
                          WHERE  a.group_number = b.group_number 
                                 AND ( MOD(a.parent_index, Power(2, 24)) ) = 0 
                                 AND a.name = '&amp;DATABASENAME') 
CONNECT BY PRIOR rindex = pindex; 


Replace &amp;DATABASENAME with your old database name and then run the scripts.

Important note: you would normally not do this. I'm sure my database has been deleted and that the remaining files are completely useless. If your intent is to clean obsolete archive logs, use RMAN instead. It's safe and really easy.