When multiple users are simultaneously sharing a workspace, it is not always clear what should happen when a user invokes an undo action. In this paper we explore different user interfaces for undo/redo for co-located collaborative workspaces, such as large interactive whiteboards. A preliminary study revealed that users expect neither a global nor personal undo, but rather a regional undo. We propose and evaluate three automatic regional undo/redo techniques (clustering, workspace, field of view) designed for a large interactive whiteboard. The results of the evaluation showed that an undo technique based on users' field of view was most preferred, while the content-based clustering technique produced most errors. We conclude with potential improvements to the developed techniques, and propose a set of design recommendations for implementing regional undo/redo on large interactive surfaces.