I know. For agile folks, that can be a dirty word. Yet XBOX Live was developed entirely using Scrum with well over 100 developers, in one-week sprints, with continuous integration, without breaking into silos.
And the resulting platform is 100 times more secure than the monolithic PlayStation online platform.
How was it done? Architecture.
Software architecture creates an API that reflects underlying information objects, captures the needs of scalability for different classes of services, and allows the front end to vary completely independently of the back end.
Software architecture allows the partitioning of functionality without losing system cohesiveness and without creating silos in your team structure.
Good architecture is the missing ingredient with most agile teams and without it, you can never be truly agile.
Hire some decent architects.