In a multisite environment, you can specify that promotions are valid only on specific sites or site groups. For example, Commerce Reference Store includes a number of site-aware promotions such as:
ATG Home – Free Shipping: This promotion is valid on ATG Home only and it gives customers free shipping when they check out from ATG Home.
Free Scarf with all orders over $200: This promotion is valid on ATG Store Germany and Site group US, which includes ATG Store US and ATG Home. It gives customers a free scarf when they spend over $200, regardless of which site they check out on.
Hubbard Chair Tiered Price Break: This promotion is valid on ATG Home and ATG Store US. It gives a price break based on the number of chairs a customer purchases.
Coupons, by default, can be redeemed on any site, however, they can also be made site-aware. A site-aware coupon can be redeemed only on those sites where its associated promotions are valid.
You make promotions and coupons site-aware using Merchandising. For details on this process, see the ATG Merchandising Guide for Business Users.