Empty temp shopping cart database

After a user adds items to the cart he doesn't checkout but leaves the site.

The next user on the same computer then opens another browser and sees the same items in the cart.

How do I Empty temp shopping cart database after leaving the site just like if I were using cookies.

Thx.when you create a record for the user you can have a timestamp column and xpire records older than 20 mins (or whatever time you decide to ) or you can empty out the temp tables before you start a new process.

hth