Item validation org in multi-org setup

Hi,

Can anyone suggest on item validation organization issue in my scenario?

OU - ABC

     IO - Unit A, Unit B

OU - XYZ

     IO - Unit-I, Unit-II

Item master org - ITM

OU - ABC

External Sales will only happen from Unit A

IR/ISO will happen between Unit A & B

Order Management Setup

Item Validation Organization is Unit A

OU - XYZ

External sales will happen from both the Units.(Unit-I & Unit-II)

Order Management Setup

Item Validation Organization is Unit-I

Unit-I sale items assigned only to Unit-I inventory org and Unit-II sales items assigned only to Unit-II

When we try to put AR invoice for Unit-II items the invoice line item LOV shows only the Unit-I assigned items. If we set the item validation organization as ITM, then all the OU items will come and make the user unclear.