How do they handle corporate intranets?

Normally I'd expect Globocorp to configure its intranet with, for example, a separate AS each for Germany and Russia. But the AS in Germany may be connected to the Russia AS via a 155 Mb/s leased line from Berlin to St Petersburg with BGP routers. The German AS may also connect via a corporate firewall to a public ISP in Germany, and the Russian AS to a public ISP in Russia.

It is theoretically possible, therefore for a user on a public ISP to connect via Globocorp's intranet to a public ISP web site in Germany.

Is there some technical or administrative requirement to prevent transit via corporate intranets?