AR showing item from different BU

Summary:

Hi Team,
Business has Four BU's.
Item assigned directly to inventory organization which is from US BU. When We tries to create Invoice in AU BU, we were able to see the item.is this expected?
How an item from one BU is showing to another BU for transaction?

Business dont have inventory, they need items directly to Invoice?/

Whats the best ideas, please advise on the same?
Thank You

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