A graphics processing unit includes a set of geometry processing units each configured to process graphics primitives in parallel with one another. A given geometry processing unit generates one or more graphics primitives or geometry objects and buffers the associated vertex data locally. The geometry processing unit also buffers different sets of indices to those vertices, where each such set represents a different graphics primitive or geometry object. The geometry processing units may then stream the buffered vertices and indices to global buffers in parallel with one another. A stream output synchronization unit coordinates the parallel streaming of vertices and indices by providing each geometry processing unit with a different base address within a global vertex buffer where vertices may be written. The stream output synchronization unit also provides each geometry processing unit with a different base address within a global index buffer where indices may be written.