Deleting item in SharePoint List – Avoid memory leakage

/// <summary>
        /// Deletes all the items from the specifid list. Uses batch processing for performance.
        /// </summary>
        /// <param name="site">The site that hosts the list.</param>
        /// <param name="list">The name of the list that has the items to be deleted.</param>
        public static void DeleteAllItems(string site, string list)
        {
            using (SPSite spSite = new SPSite(site))
            {
                using (SPWeb spWeb = spSite.OpenWeb())
                {
                    SPList deleteList = spWeb.Lists[list];

                    while (deleteList.ItemCount > 0)
                    {

                        SPQuery query = new SPQuery();
                        query.RowLimit = 500;

                        SPListItemCollection collListItems = deleteList.GetItems(query);

                        StringBuilder sbDelete = BuildBatchDeleteCommand(deleteList, collListItems);

                        spWeb.ProcessBatchData(sbDelete.ToString());

                        deleteList.Update();
                    }
                }
            }
        }

private static StringBuilder BuildBatchDeleteCommand(SPList spList, SPListItemCollection collListItems)
        {
            StringBuilder sbDelete = new StringBuilder();
            sbDelete.Append("<?xml version=\"1.0\" encoding=\"UTF-8\"?><Batch>");

            string command = "<Method><SetList Scope=\"Request\">" + spList.ID +
                "</SetList><SetVar Name=\"ID\">{0}</SetVar><SetVar Name=\"Cmd\">Delete</SetVar></Method>";

            foreach (SPListItem item in collListItems)
            {
                sbDelete.Append(string.Format(command, item.ID.ToString()));
            }
            sbDelete.Append("</Batch>");

            return sbDelete;
        }