i believe for corporate environments it's a VERY strong knowledge of the entire company's technological infrastructure.

Including but not limited to:
-Networks (usually the #1 prerequisite)
-Databases
-Intranets
-email systems
-Security
-websites
-legal issues

However, it's not just the knowledge of the above, it's MANAGING every little aspect of each and every bit of it.

But at even more at a director level, you should also have a very strong working knowledge of accounting/finance, budgeting, purchasing, aquisitions, and hiring.

From my short personal experience in large corporate environments, if you're not a former networking/programming engineer, you're not really cut out to be a director of technology.