Exactly exportvg will clean the ODM and remove entries in /etc/filesystems.
If you have some disks that are on the system not assigned to any VG
you can check if they were assigned to any VG by reading
Volume Group Descriptor Area on the disk
It is "readvgda" command
More info here:
https://www.ibm.com/developerworks/m...dvgda3?lang=en