Why don't blocks show up in the buffer cache after performing a query?

I performed a query (see below) to view the contents of my buffer cache to see how much of a particular table was cached.  I noticed the table/object wasn't returned in the query.  I wrote a SELECT * FROM tabname and then re-performed the query and noticed that there were still no blocks in the buffer cache from the table ("tabname") that I just queried.  Why is this happening?  Why don't I see any blocks in the buffer cache?

Thanks,

Greg

select

s.owner owner,

object_name objname,

subobject_name subobjname,

substr(object_type,1,10) objtype,

ts.block_size / 1024 blockkb,

buffer.blocks blocks,