when the checkout form posts to the confirm page, the shipping country is stored in a session variable named:
you would need to create separate shipping rules for each price break, for domestic and international.
the rules will set the price breaks by using the Based on taxable total trigger, but then add another trigger for session Variable is set "eCartCheckoutForm_shipping_country" and Based on Session Variable value.
for the domestic shipping rules use:
session variable "eCartCheckoutForm_shipping_country" is "=" a value of "US"
for the international rules use:
session variable "eCartCheckoutForm_shipping_country" is "!=" a value of "US"