The object flowing down the pipeline is responsible for storing validity intervals for each channel. The validity interval is used by 3ds Max to know whether or not it can use the world space cache.

Consider a sphere object with an animated radius parameter. The validity interval for the geometry channel for this sphere will be instantaneous (valid for a single TimeValue). This is because the radius is animated and is thus always changing. However the topology channel of the sphere is never changing. Therefore the validity interval for the topology channels will be FOREVER.

See the topic on Intervals for more details.