@@IDENTITY is a system function that can be used to retrieve last inserted identity value. @@IDENTITY is not limited to scope.

for example, I have a Table which contains an identity column as below:

-- © 2011 – Vishal (http://SqlAndMe.com)
 
USE [SqlAndMe]
 
CREATE TABLE [dbo].[Temp](
      [IDNum]     INT IDENTITY(100,1) NOT NULL,
      [Name]      NCHAR(10) NULL
)

After I insert new row to table, I can use this functions to retrieve the inserted identity value.

-- © 2011 – Vishal (http://SqlAndMe.com)
 
INSERT INTO dbo.Temp VALUES ('Ahmedabad')
INSERT INTO dbo.Temp VALUES ('Bangalore')
INSERT INTO dbo.Temp VALUES ('Reading')
 
SELECT @@IDENTITY AS 'Last Inserted'

Result Set:

(1 row(s) affected)
 
(1 row(s) affected)
 
(1 row(s) affected)
Last Inserted
—————————————
186
 
(1 row(s) affected)

@@IDENTITY only returns the last identity values inserted in case of multiple inserts.

SCOPE_IDENTITY() as the name suggests is limited to the same scope in which last identity value was inserted to a column. SCOPE_IDENTITY() should be used if you need to retrieve the last inserted value from the table you inserted the rows explicitly.

Another useful function for this task is IDENT_CURRENT().

Hope This Helps! Cheers!