Intel announced it will stop taking orders for the last of its Pentium 4 and D processors in December:
From 5 October, orders for tray-packed and single-CPU boxed Pentium 4 631, 641 and 661, and Pentium D 915, 925, 935 and 945 processors will not be allowed to be cancelled - a warning to customers that they really must be sure they want these chips after that date. After 7 December, Intel won't be taking any orders for these CPUs at all.
That allows Intel to wind down production from 5 October quickly or slowly depending on how many fixed orders it has outstanding. Not too many for desktop PCs, we'd reckon given the availability of cheap Core-based dual-core CPUs under the Pentium brand.