How to force JBoss 4.2.3 to clear hibernate's session cache for every request?

问题

It seems to me that JBoss reuses entity managers and the underlying hibernate sessions for multiple requests. I have run a test which proves that in some cases the state of an entity may be out-dated even if it is just fetched using em.find().

How can I disable this behaviour and force to clear or throw away used sessions to ensure that each request is handled with clear cache?

UPD:

Here is an example case.

HTTP request 1. A session bean creates an entity instance and stores it with field "A" set to value 1. The persisted entity gets ID = 4.

HTTP request 2. A session bean looks up an entity with ID = 4, sets its field "A" to value 2 and saves it.

HTTP request 3. A session bean looks up an entity with ID = 4 and checks it's field "A". If the value is 1 it does one thing, if it is 2 it does another thing.

In case if the EM in request 3 happens to be the same as in request 1, an undesired behavior occurs. I have tested this and got approx. 10% cases of failure.