Post Cereal $1.00 a box at Walgreens

Yet another great Walgreens Register Reward deal. This one appears to be a hidden deal. It's not advertised in the weekly ad:

Post Cereal is on sale 2 for $5.00 this week
Purchase 4 Grape Nuts cereals for $10.00 total
Use two $1.00 off 2 coupons from the 3/1 SmartSource insert
Pay $8.00 Out-of-Pocket
Get back a $4.00 Register Reward
Final cost ONLY $1.00 per box!

(I have only found this to work on the Grape Nuts cereal - no other brands at this time - I will update if I find something otherwise)