Declare @MaxID int,
    @CurrID int,
    @SQL nvarchar(100)
Declare @DBs Table (DBID int identity(1, 1) not null primary key,
                    DBName sysname not null unique)

Set NoCount On;

Insert Into @DBs (DBName)
Select name
from sys.databases
-- 0 = online
Where state = 0
-- Not a snapshot
And source_database_id Is Null
-- Not marked read-only
And is_read_only = 0;

Select @MaxID = MAX(DBID),
    @CurrID = 1
From @DBs

While @CurrID <= @MaxID
  Begin
    Select @SQL = 'Use ' + QUOTENAME(DBName) + ';
        If OBJECT_ID(''dbo.MyProcedure'') Is Not Null
            Exec dbo.MyProcedure;'
    From @DBs
    Where DBID = @CurrID

    Exec sp_executesql @SQL;

    Set @CurrID = @CurrID + 1
  End

Set NoCount Off;