Transferring rows between 2 databases on 2 web servers

Hi Everybody, There are n number of web servers all having the same Linux-Apache-MySQL-Php setup, with identical databases. Each of these servers functions as a billing server at a store of my company. Now I am required to set up a master server that will copy all data from each of the store servers. All I wish to know is: How can a page on the master server obtain data from a store database by calling a page located on the store server? I do not wish to access a store database directly, but through a page on the store server. Specifically, how can a web page get data from another web page on another server. Many thanks, Ferdi