How to create procurement BU without any link to Legal entity ?

Summary:

For our client, we would like to have 2 procurement BU (one for each country) as a centralized service

Content (required):

We have 10 Requisitioning BU in 2 differents countries and we need to create 2 Procurement BU (one for each country) as a centralized service, these procurement BU will be used to transform the Requsiition to PO (automatically), to create agreements, ...

• Do we need to create an inventory org. for these procurement BU ?
• Is it mandatory to link these procurement BU to one legal entity ? because these procurement BU will manage many

Requisition from different LE and we don't need to link them to one entity