Marty Cagan continues his excellent product autonomy series by discussing what happens when teams get large enough to split up their code bases. In Autonomy vs. Ownership he describes his preferred way of dealing with the situation where a team needs a change in a different codebase to get one of their features implemented:

The alternative model is informally known as the “open source” model although to be clear this is not about open sourcing your code, it’s just called that because this is how much of the open source community operates. In this model, if the drivers team needs a change to the riders team’s code, then they could either wait for the riders team to do it, or they can actually make the change themselves, and then request that the riders team review the change, and include it if they’re okay with it (known as a “pull request”). This means that you are telling the software management system that you’ve made a change to the software, but the owner of that software needs to review the changes before they are actually approved and incorporated.