Godhelp,
Can you provide more details on your scenario? Do you have central incoming payment process where IHCC / headoffice collects subsidiaries' customer payments in its external account? Or are you trying to post credit to subsidiary's IHC bank account for cash movement / ZBA from subsidiary's external bank account to headoffice / IHCC?
In second scenario, normally headoffice external bank statement has a unique identifier in payment notes which allows you to identify correct subsidiary account for credit in IHCC. Please check IMG settings for Central Cash Receipt / Incoming Bank Statements.
Thanks
Amit