Data caching with multiple HTTPApplication instances

[rbg]

Have a web application which uses Data Cache.
I need to understand what happens when a new instance of the same web
application is created for
for serving concurrent clients.
What happens when the data in the cache expires (either due to
expiration or due to dependency change)
do all instances of the Http Application replace the cached data at the
same time.
Thus what I am essentially asking is, in a single server scenario if
multiple instances
of the same web application are created in the App Domain of the
aspnet_wp.exe
worker process should we be concerned with storing data in the data
cache.

On similar lines when we use application State and use lock and unlock
statements to do thread safe modifications to the data in Application
state, wouldn't other instances of the same HttpApplication allow
modification of the data at the same time. Thus I do not understand how
Application state works if multiple instances of the same Application
are created for serving concurrent clients.

Is it true that aspnet_wp.exe worker process spawns multiple instances
of the same HTTPApplciation?
Also how and when does the aspnet_wp.exe worker process spawn a new
instance of the
HTTPApplication class(a new instance of the same web application)

Also what happens in a Web garden scenario. I do not understand why
Storing data in
the data cache would be affected if it is a web garden where a machine
has multiple processors.