Flash CS5.5 Professional.
fl.publishCacheMemorySizeMax
Property: an integer that sets the maximum size, in megabytes, of the publish cache in memory.
The following code sets the maximum publish cache size in memory to 1 megabyte:
fl.publishCacheMemorySizeMax = 1fl.publishCacheDiskSizeMax, fl.publishCacheEnabled, fl.publishCacheMemoryEntrySizeLimit, fl.clearPublishCache()